As the United States withdraws its combat forces from Iraq and begins a similar drawdown in Afghanistan, Iran is rapidly broadening its reach and presence in and beyond the region — and its technological prowess in weaponry — to undergird a strategy of global proportions, to threaten Americans at home and abroad as well as our overseas friends and allies. As the United States draws down its presence in the region, Iran is moving to fill the resulting power vacuum. U.S. missile-defense plans and programs need to adapt to the likely consequences, including an increasing threat to the U.S. homeland and broadening Iranian influence in the Middle East.

In his July 2011 quarterly report to Congress, Stuart W. Bowen Jr., U.S. special inspector general for Iraq reconstruction, concluded that “Iraq remains an extraordinarily dangerous place to work. . . . It is less safe, in my judgment, than 12 months ago.” This is in no small part due to Iran’s growing involvement in the Iraqi conflict — which is likely to grow further as U.S. troops are withdrawn.

Last summer, Adm. Mike Mullen, then chairman of the Joint Chiefs of Staff, observed that “Iran is very directly supporting extremist Shiite groups which are killing our troops” in Iraq. (The Taliban, meanwhile, has used rockets obtained from Iran to target NATO and U.S. forces in Afghanistan.) And in his final statements as secretary of defense, Robert Gates noted that about 40 percent of American servicemen killed since the end of U.S. combat operations last fall were killed in attacks by Shi’ite militias armed, trained, and funded by Iran.

In his confirmation hearing, Gen. Martin Dempsey, the current chairman of the Joint Chiefs of Staff, noted that recent activities “are intended to produce some kind of Beirut-like moment . . . and then in so doing to send a message that they have expelled us from Iraq.” Thus is the stage being set for Iran to dominate the future development of Iraq.

Iran has also supported uprisings where they weaken U.S. influence and opposed them where, as in Syria, they diminish Iran’s own position. But if uprisings of the latter sort gain the upper hand, Iran is quick to moderate its opposition and seek accommodation. While troublesome, these tactical moves are just part of a larger and more threatening Iranian strategy that is rapidly becoming clearer — one that includes a central role for nuclear weapons.

The head of Iran’s Atomic Energy Organization, Fereidoon Abbasi, has reported that by the end of this year, Iran will triple the amount of uranium it has enriched to a level of 20 percent. Although uranium enriched to this level may fuel Tehran’s small nuclear-research reactor, which produces medical isotopes, it also bolsters the knowledge of Iranian nuclear experts and their ability to master all stages of enrichment, including to the higher levels needed to produce a nuclear weapon. Thus, as an International Atomic Energy Agency (IAEA) report issued in June indicates, Iran is accelerating the pace of its nuclear-weapons program.

This has implications for Iran’s geostrategic aspirations in the Middle East and far beyond. For example, recent Turkish hostility to Israel is, in the opinion of many, all about Turkey’s relationship with Iran. Turkey is now developing and exploiting its Iranian connections while seeking to balance these with the interests of its NATO partners — e.g., Ankara has agreed to base a radar in Turkey, to help defend NATO territory against Iranian ballistic missiles, while sometimes opposing the tracking of missiles from Iran.

The July 29 mass resignation of high-ranking Turkish military officers (including the four most senior ones) signaled a significant shift from Turkey’s secular government toward one likely to be less friendly to Western democracies and more friendly to Islamist states such as Iran. This trend bodes ill for Turkey’s willingness to defend NATO territory from Iranian missiles.